This invention relates to prostheses for surgical reconstruction of the auditory ossicles of the middle ear which provide mechanical lever advantage to the transmission of sound pressure into the inner ear. This provides repair of conductive hearing loss with permanent restoration of normal hearing, with both short-term and long-term stability of the prosthesis after implanting, and avoids the danger of extrusion through the tympanic membrane (ear drum) as well as excessive pressure on the oval window of the inner ear.
The prostheses of the invention are fabricated from materials which are biologically inert, i.e., no resorption and no host reaction such as inflammation, foreign body reaction or scar tissue.
The prior art has utilized bone transplants for replacement of portions of the ossicular chain in the middle ear. Although this is considered the most reliable procedure at present, it suffers from serious disadvantages, viz., loss of the middle ear mechanical amplification of sound and therefore less than normal hearing restoration, instability of reconstruction resulting in progressive worsening of hearing as the prosthesis migrates, resorption of bone, and excessive pressure on the oval window causing dizziness.
Various synthetic polymeric and metallic prostheses have been used in the prior art. These have generally met with long-term failure (2-3 years after implantation) with consequent loss of hearing because of instability, extrusion through the tympanic membrane, or biodegradability.
Short-term hearing restoration was reported for TORP and PORP synthetic ossicles, but only 15%-25% of these implants maintained satisfactory hearing five years postoperatively.
U.S. Pat. No. 3,710,399 discloses a prosthesis for surgically replacing the malleus, incus and stapes of the middle ear, comprising two biochemically inert wire struts mechanically held in parallel partly overlapping relation, with one end to be surgically attached to the tympanic membrane and the other end to be attached to the oval window, the struts being magnetically coupled to transmit sound oscillations. This prosthesis to does not have a mechanical lever advantage to amplify sound and would tend to be unstable, to extrude through the tympanic membrane and to place excessive pressure on the oval window.
U.S. Pat. No. 4,130,905 discloses an artificial malleus columella for the human ear comprising an elongated member angled downwardly to provide first and second linear portions, a stem extending from the underside of the first linear portion to contact the stapes when installed, and a clamp located on the external surface of the angle and extending over the second linear portion to engage the bridge of the ear. This prosthesis has not been used successfully because it does not amplify sound, is cumbersome to use, and would tend to be unstable.
U.S. Pat. No. 4,215,438 discloses a prosthesis intended to connect the incus and stapes, comprising a goblet-shaped member having an open cup-like end adapted to receive the capitulum of the stapes, and an integral stem adapted to be inserted in a hole drilled in the incus. Preferably the prosthesis is of stainless steel. It is apparent from the above summary of the disclosure that this prosthesis has utility only as a replacement for the damaged lenticular proces of the incus. It is surgically extremely difficult to drill a hole into the incus without disruption of the incudo-mallear joint and thus the integrity of the ossicular chain.
Despite the extensive studies devoted to auditory ossicular reconstruction and the numerous prostheses which have been proposed and tested, there is not now an available prosthesis which permits single-stage ossicular reconstruction for all combinations of middle ear ossicle damage and which provides in combination a lever advantage equal to or greater than natural hearing, stable short-term connection between the malleus and the inner ear preventing loss of vibrational energy and rotation of the prosthesis, avoidance of extrusion through the tympanic membrane, long-term stability due to ingrowth of host bone into the porous surfaces of the prosthesis, biologically inert materials, a single size prosthesis for replacement of the incus adaptable to any size human ear, stability of connections to existing ossicles by laser welding or bonding adhesives, and reduction of pressure against the oval window eliminating dizziness and the risk of inner ear fluid leak with consequent infection.